1. Field of the Invention
This invention pertains to the field of thin-walled plastic food containers having a base and a lid engaging the base so as to form a peripheral seal.
2. Description of Related Art
Food containers in the above-identified field often include a base and a lid made of plastic sheet material, each having a peripheral sealing region, with a downwardly facing channel generally shaped like an inverted “U”. The respective channels of the base and lid mate and engage to form a seal. Such containers often have two or more seals, which are referred to as “primary”, “secondary”, etc., according to their proximity to the contained product. Examples of such containers are described in Littlejohn U.S. Pat. No. 5,377,860, Chen U.S. Pat. No. 6,056,138, Tucker et al. U.S. Pat. No. 6,910,599, and Stanos et al. U.S. Pat. No. 7,063,231.
Fundamental requirements of such food containers include tightness and reliability of the seals, in order to prevent spillage and leakage of contained liquid products. Less fundamental but also important is ease of closing, opening, and re-closing the lids, since a seal that has the desired degree of mechanical tightness may be difficult to open without spilling the contents of the container. Often this is due to the suddenness of the release, coupled with the lightness and flexibility of the container. In addition to these requirements, there are the usual objectives or requirements of cost, durability, strength, appearance, etc., as is the case with nearly all consumer products.
Various features have been proposed to achieve an acceptable balance of these requirements and objectives. The above-identified Littlejohn patent discloses in FIGS. 7-10 a frustoconical lid seal area 68. The above-identified Chen patent discloses in FIG. 5 a lid locking lip 44 contacting a base sealing edge 39. The above-identified Tucker et al. U.S. patent discloses in FIGS. 17C and 17F two opposed area seals. The above-identified Stanos et al. patent discloses in FIGS. 2-4 a seal ring 36 on the horizontal surface of the U-shaped channel of the base or lid.